Evidence about electronic cigarettes: a foundation built on rock or sand?

Evidence about nicotine toxicity and the dry puff phenomenon

Grimsrud wrote an alarming comment about the negative effects of nicotine on cancer disease. He cites a review by Sanner and Grimsrud about the nicotine effects on cancer [1]. It is characteristic that all evidence in that review was derived from cell and animal laboratory studies. On the contrary, their discussion about human effects was only related to smoking or oral tobacco use and not to nicotine. Another recent review on nicotine carcinogenicity by Grando [2] cited an impressive number of studies, all of which were again laboratory studies. It is characteristic that in many (if not most) cases the amount of nicotine used in the experiments is by far larger than applicable to human smokers. Characteristically, Grando cited one of his own studies in which he tried to reproduce the daily dose of nicotine consumed by Scandinavian snus users in A/J mice through subcutaneous injections [3]. Impressively, the nicotine dose was lethal for 50% of the animals (LD50), clearly showing that the experiment was irrelevant to human effects. Another study linked nicotine with breast cancer, but exposed cells to 5mM of nicotine which is about 20,000 times higher than plasma nicotine levels in humans [4].

In that context, it is surprising and worrying that scientists pay so much attention to laboratory studies but ignore human epidemiological data. The Lung Health Study followed-up long term nicotine users for 7.5 years and found no elevated incidence of cancer [5]. The evidence of snus is extensive and convincing. Snus use is associated with minimal cancer risk, for which nicotine probably plays no role [6-8]. For these reasons, major health organizations have recommended the long-term use of pharmaceutical nicotine products as substitutes to smoking. Smoking pregnant women are also included in those who could use nicotine replacement therapy for smoking cessation [9,10]. It would be at least ironic to discourage pregnant women who cannot quit smoking “cold-turkey” from using nicotine replacement therapy, allowing them to be exposed to the thousands of toxins present in cigarette smoke. Thus, the whole issue about the risks of nicotine is of minimal concern and, thus, irrelevant and misleading when discussed in the context of continuous smoking. As for never smokers, the scientific community has unanimously made it clear that nicotine use is not recommended for this population.

Bareham quotes some statements from Goniewicz, which represent legitimate but theoretical concerns. Many scientists (including myself) have repeatedly supported that monitoring of use by non-intended population (never smoking adults and youth) is important and that measures to avoid use by this population but promote use by smokers are needed. But this is different from supporting that use by non-intended population is really happening at any level besides experimentation. It is becoming common for studies to discuss about nicotine addiction from e-cigarettes and subsequent gateway to smoking, but it is shocking to see that in reality neither regular nor nicotine use was assessed in those studies. [11,12]. One of them [12] was even accompanied by an editorial titled: “Electronic cigarettes are another route to nicotine addiction in youth” [13], while there was absolutely no evidence that the study subjects used nicotine-containing e-cigarettes or became addicted to e-cigarette use, since none of the these were assessed in the study. This represents a classic example of distortion of science, which is reaching unprecedented levels in the case of e-cigarettes. Until recently, this was observed only in press releases and the newsmedia, but now it seems to be happening to scientific publications.

Finally, Bareham presents the argument that flavoured e-liquid may mask the dry puff harsh taste observed when liquid is overheated. This argument is invalid for a simple reason: the dry puff phenomenon was originally observed and detected by e-cigarette users, not by scientists. Every experienced e-cigarette users known this phenomenon, and it was much later (in 2013) that the phenomenon was presented and explained in scientific literature [14,15]. It is well-known that the vast majority of e-cigarette users use flavoured e-liquids, thus the phenomenon is observed with flavoured e-cigarettes. Obviously, more studies are needed to further characterize this phenomenon; however, it is more reasonable to generate conclusions based on currently available evidence rather than focus only on concerns that remain unsupported by evidence.